1. Field of the Invention
The invention relates to a latch assembly and method for latching, unlatching and relatching of two tubing conduits, typically defined in a production or other tubing string for use in a subterranean well. The assembly may be utilized to, for example, release or re-engage a tubing string relative to a production tubing hanger. The latch assembly also may be used to hydraulically activate an auxiliary tool.
2. Description of the Prior Art
In the production of well fluids, such as oil and/or gas, from wells, it has been the practice to provide automatically closeable shut-off or safety valves which are located downhole in the well and are held open by control fluid pressure, the valves closing automatically when control fluid pressure is purposely reduced to allow the valves to close or damage occurs to the control fluid system at the well head or on an offshore platform. Such valves are employed below the well head, and in the case of offshore wells, the valves are installed below the mud line at such depth as may be desired or established by regulation, so that in the event of damage of the well caused by shifting earth or subsidence, or well head catastrophe, the well can shut in to avoid loss of valuable well fluids into the water, and also, to avoid contamination of the water and the shore.
Many offshore wells are produced from spaced well zones through separate strings of production tubing, and a safety or shut-off valve is required for each zone. Since, from time-to-time, it is necessary to perform various remedial operations through the tubing strings, it is preferred that the safety valves be easily removed from the well for service or repair. Accordingly, commercially available safety or shut-off valves have been provided which have been run into the well casing on production tubing and landed in a tubing hanger which supports the greater weight of the downwardly extending production tubing strings. Typically, such a tubing hanger has been run into the well casing on a setting tool to a desired location, and, in the case of an offshore well, to a prescribed depth below the mud line. In such an apparatus, the tubing hanger is anchored in the well casing and the setting tool is released from the tubing hanger and removed from the well. The tubing hanger provides a seat for the safety or shut-off valve assembly which is run into the well on an upward extension of the production tubing and landed in the tubing hanger, subsequent to the setting of the hanger and retrieval of the hanger setting tool.
The necessity of two trips into the hole with work strings and/or other means to first carry and anchoringly set the tubing hanger and thereafter land the conduits containing the safety valves therein is an economic deterrent since considerable rig time is expanded in running a first work string and/or other means for anchoring the hanger, retrieving the work string and/or other means, and thereafter running the production tubing containing the safety valve or valves into sealing engagement with the hanger.
The present invention obviates many of the problems typified by prior art, commercially available apparatuses, and is an improvement thereto by providing a latch assembly which may be utilized, as described below, in one embodiment, to engage an upper tubing string section extending from the surface of the well into sealing engagement with a tubing hanger or a conduit below the latch assembly.
The latch assembly incorporates means for hydraulically releasing the latch assembly for retrieval of the conduit extending to the top of the well which has been initially sealingly engaged with a lower conduit. The latch assembly also has auxiliary mechanical disengaging means which may be activated in the event of failure of the latch assembly to disengage from the lower conduit by hydraulic means.
In an alternative embodiment, the latch assembly also incorporates hydraulic means for setting of an anxiliary tool, such as a tubing hanger, to anchor the auxiliary tool to the well casing. Thus, the auxiliary tool may be set hydraulically without the use of a wireline activated or other separate setting tool.
The mechanical release backup feature of the latch assembly alternatively incorporates a swivel sub apparatus which permits rotation of the section of conduit immediately above the latch assembly when the conduit above the latch assembly is not easily rotatable because of, for example, securement against rotation into a surface hanger at the top of the well.